Envelope reads "Hetch Hetchy Mitchell tunnel explosion 7/17/30." Phogograph shows a man seated facing left. He wears a checked overshirt and no hat. The Mitchell Tunnel explosion was the second major blast to rock the hills outside of Livermore in Alameda County in the summer of 1930. Following closely on the June 9 accident at the nearby Calaveras Tunnel site, 36 walked off the job after this second accident killed 12 workmen on the morning of July 17. Survivors compared the explosion of gas inside the tunnel to an earthquake, and the bodies of the dead were blown 200 feet from the tunnel entrance. The accumulated gas was likely ignited by a spark from a match or cigarette used in the tunnel, though many blamed lax enforcement of safetly regulations for the which allowed the gas to collect. Information from articles in the Oakland tribune July 17-20, 1930. For more information about Hetch Hetchy see h99.1.470. This photograph was printed in the Oakland Tribune on July 17, 1930 with the caption "R. A. Trompczynski, one of the rescued.